1. Field of the Invention
This invention generally relates to a method of constructing orchid haploid by treating unfertilized orchid flower with auxin.
2. Description of the Related Art
Orchid is always very popular as a flower for enjoyment, in recent years, and a mass cultivation is performed in order to meet the demand for supply. As a popular reason, in accordance with a consumer's taste, a variety of orchid with sufficient economical efficiency which can be tolerated to the mass cultivation have been developed. These varieties of orchid have been developed by traditional cross-breeding. This cross-breeding means selecting any superior individuals from a seedling group which was obtained by mating. The obtained superior individuals need to propagate to a level suitable for mass consumption, and a cloning by tissue cultures is used as a mass propagating method.
The technology of the cloning by tissue cultures is still unstable, and has problems, such as difficulty depending on the varieties of orchid, and any mutation in tissue cultures. In order to avoid these problems, solutions which suppresses a proliferation rate of cloning which performs experimental proliferation of cloning for every each varieties of orchid is used. However, neither of the ways can suppress a generating of mutation completely, but a generation of any malformated flower is found in orchid of the proliferation of cloning by tissue cultures.
This mutation is caused by the cell proliferation which is not considered in natural circumstances where it is performed in a stage of tissue culturing. By contrast, there is very little generating of mutation in the division method by natural proliferation of plants performed in the past. However, it is difficult for the proliferation rate to be suppressed with very low rate and to cope with mass consumption in recent years by the division of plants.
Although propagation that there are no mutational problem and that the high rate of proliferation is obtained by generally using seeds for propagation is performed, since orchid plants have high hybridization rate, the homogeneity in a seed propagation group has a notable problem. Thus, there is a method using haploid plants as one way of improving the homogeneity in this seed propagation group.
As for haploid plants, it is possible to have a doubled gene by colchicines treatment. Plants having a doubled gene are pure line plants and a uniform seed propagation group is obtained by performing self-mating of these pure line plants. Furthermore, there is no hereditary difference between individuals in the first hybrid (F1 plant) obtained by mating between pure line plants, it is possible to obtain uniform future generations, and the uniform seed propagation group can be also generated from this F1 hybrid.
Since these seed propagation groups are not only uniform, but also there is little risk of mutation due to not performing the proliferation of cloning by tissue cultures, and the desirable additional characteristics, such as heterosis, are also expected in seed propagation groups obtained from the F1 hybrid. As for the proliferation of cloning by tissue cultures, since a culturing period will become long when mass proliferation is performed from the same tissue cultures, although the risk of mutation also becomes high, mass propagation is achieved in a seed propagation group for a short period of time.
As for the method of constructing haploid, although it is effective only in a specific plant, generally, an anther culture method and an interspecies crossing method are established. Although the method of constructing haploid using the anther culture method is available for breeding tobacco, rice and wheat, and the method of constructing haploid using the interspecies crossing method is available for breeding potatoes, barley (Hitoshi Kobayashi, 1987, “New plant breeding technology”, Yokendo, pp. 110-112), it has not been recognized that the method of constructing haploid is applied to the variety of orchid.
On the other hand, auxin is one of the plant growth regulators (plant hormone), one of the action has fruit bearing without pollination and hypertrophy growth of fruits. It is found that when plants are treated with auxin, even if not fertilized, fruits will occur parthenogenesis which take places hypertrophy growth, and will continue to grow (Shin Kuraishi, 1988, “plant hormone”, second version, Tokyo University Shuppannkai, pp. 45-46). This action is applied to a culture of tomato, even if pollination is not performed, set of fruits and hypertrophy are performed with auxin to an unfertilized flower of tomato. This is because of the action of auxin, the parthenogenesis is induced and an unfertilized ovary grows. However, the high concentrated auxin will induce a generation of ethylene and make fruits fall off plants, thus unless it is moderate concentration of auxin, an unfertilized ovary will fall, then seeds cannot be obtained.
When pollens of calanthes and cymbidiums are mated to Bletilla striata which is one variety of orchid, many seeds will be obtained easily. However, when these seeds are planted, judging from its germination and a feature of its seedling, the possibility of parthenogenesis is very high. This would be due to ploidy parthenogenesis of egg cell from which the ovary developed by stimulus of pollens hormone or forming seeds by apogamy in which embryo originates from nutritional tissues of mother's bodies, such as placenta (Itsuhiko Ito, Koji Karasawa, 1969, “Calanthe and its group”, Seibundo-sinkosha, pp. 296-207).
Moreover, it is reported that parthenogenesis has been induced by giving naphthaleneacetic acid which is one kind of auxin to stigma of Zygopetalum which is one variety of orchid (Genjiro Mori, Koichi Yamaoka, Hideo Imanishi, 1989, “Studies on the possibility of including apomixis in some orchids”, The magazine of horticulture society, second additional version of volume 58; Genjiro Mori, Koichi Yamaoka, Hideo Imanishi, 1991, “Seed formation of Zygopetalum mackayi by apomixis”, The magazine of horticulture society, second additional version of volume 60, pp. 466-467).